The present invention relates to chemically reactive security ink, a method of using such ink, and documents incorporating such ink, and more particularly to such ink, method, and documents in which fraudulent changes to security documents may be made obvious.
A number of approaches have been taken in the past to thwart or reduce the fraudulent modification of security documents. It has been common for criminals to modify a security document, for example increasing the value of a bank check, by applying a solvent to the security document to remove a portion of the valid written information from an area of the document and then typing, printing or writing altered information into the same area on the document. Various approaches have been taken in an attempt to make such document alterations noticeable and, therefore, ineffective. U.S. Pat. No. 6,306,929 teaches a bleeding ink that is used for printing security documents. The '929 patent discloses bleeding inks having non-drying vehicles, as well as using dyestuffs sensitive to organic solvents and other chemical agents. The '929 patent suggests the same dyes used in known bleeding inks, such as Solvent Blue 67.
U.S. Pat. No. 5,601,683 to Martin teaches printing a void pantograph in dye-based, solvent-sensitive inks that wash away with acetone or bleach. U.S. Pat. No. 5,209,515 to Dotson et al teaches a solvent sensitive ink which reacts to the application of a solvent or pressure to form a visible stain, image, or warning indicia, such as for example the word “VOID”. It may be printed as repeating text, a spot, or as a full coating. The '515 patent discloses an ink that changes from colorless to a color, providing a covert security feature. The ink remains invisible until it is attacked by solvent. It is known that some solvent-sensitive void coatings of this sort will wash away completely if soaked long enough.
U.S. Pat. No. 5,636,874 to Singer teaches a feature that can be used for authentication and validation. Temperature-sensitive ink is printed over a temperature-insensitive message, both inks being of the same color. When the document is rubbed or heated, the temperature sensitive ink turns colorless and this reveals a message such as “VALID” underneath. Upon cooling, the color returns once again, masking the message.
Various chemically reactive inks have been used for security purposes. Bleeding inks, erasable inks, coin-reactive inks, transparent inks, pen-reactive inks, transparent inks, heat reactive reversible and irreversible inks, infrared inks, optically variable inks, photochromic inks, and ultraviolet invisible fluorescent inks all offer ways of either authenticating by effecting a change in appearance under controlled circumstances, or provide protection against fraud by making undetected alteration more difficult.
In another alteration technique, called check washing, a check is fraudulently altered after washing it with any of a number of chemical cleaners to remove the valid data. This most commonly occurs with handwritten checks. Check washing is less commonly used with commercial checks that are printed with a toner ink, since a solvent may not be as effective as scraping and picking the toner from the check surface mechanically.
It is seen, therefore, that a need exists for an improved ink and method of use of such ink, as well as an improved security document, in which alterations to the security document are made more obvious such that the fraudulent use of the document is prevented or made more difficult.